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Mission (almost) Impossible: Why is it so hard to weld cast metal?

One of the most frequently asked questions we get here at All Metals Fabrication is whether we can weld cast aluminum or cast steel. There are a couple of reasons why this is not possible, and this blog will give a thorough, yet quick, explanation of why this is.

Impurities. Impurities are the main reason that welding cast aluminum or cast steel is a bad idea. Castings are notorious for being porous, and when they are heated up the pores that were created during the aluminum forming process bubble up and lower the integrity of the piece. Unfortunately, impurities are very hard to predict and can come from almost anywhere. Factors like the humidity present during a weld, or lubricants that were used, can all play a significant role in the amount of pores or impurities on a piece.

Castings. Castings get their name because they were (you guessed it!) cast. That means that the metal was originally in a different form or shape. Casts can cause problems with heating and re-heating. Some areas of a cast will heat up quicker than others based on how thick or thin they are. As parts of a casting heat up, the chances of the metal cracking are much greater.

Preheating. While welding cast steel and cast aluminum is possible, it requires very close attention to detail and very specific steps. Preheating is one of the most important steps in the cast welding process. The entire casting needs to be heated at between 500-1200 degrees F. The slower the heating process the better, as impurities and cracks have a lesser chance of showing up. Once you are ready to weld, it’s better that you use a low current. A good place to start is with a 4043 tig rod, as it tends to prevent porosity and has a higher silicon content.

Just remember, if you are dealing with cast metals, you will have a much more difficult time fabricating them. Casting means impurities and impurities can lead to pores and other welding issues.

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